Prostate cancer is one of the most commonly diagnosed cancers in men. Although prostate cancer can be detected with a blood test for high prostate-specific antigen (PSA) levels, high PSA levels can also result from non-malignant growth of the prostate. The most accurate diagnosis of prostate cancer is obtained by analyzing a stained prostate biopsy using the Gleason grading system. The Gleason grading system was developed by Donald Gleason, a pathologist at the Veterans Administration, and correlates patterns in prostate biopsy specimens with tumor mortality rates.
The Gleason grading system evaluates the glandular architecture of the prostate tissue. Tissue is assigned a grade based on the overall pattern of the glands as well as the shapes of the individual glands. Malignant cells disrupt the regular pattern of the glands. Glands arranged in a disorganized, irregular pattern with only a small area of stroma between the glands are diagnosed as cancerous. In addition, tissue in which fewer of the individual glands are circular is also diagnosed as cancerous. Cancerous prostate tissue is classified into five grades 1 through 5 of decreasing regularity and circularity. The grades of the two patterns that cover the largest areas of the biopsy tissue are added to obtain the Gleason score.
The primary Gleason grade must be greater than 50% of the total pattern of the cancerous tissue. The secondary Gleason grade must be less than 50%, but at least 5%, of the pattern of the total cancer observed. If the secondary pattern covers less than 5% of the total area of observed cancer, the secondary grade is assigned the same grade as the primary grade. The sum of the primary and secondary Gleason grades is the Gleason score. For example, if the most prevalent pattern falls into grade 4 and the second most prevalent pattern falls into grade 3, then the Gleason score is 7.
Gleason grading is typically performed by a pathologist who visually evaluates a magnified image of a stained tissue sample. The pathologist manually inspects each cancerous area of a slide of stained tissue, classifies the patterns of the glands in each area based on the shape of the individual glands and the arrangement of neighboring glands to one another, and assigns a Gleason grade to each area of the tissue being graded. Then the pathologist determines an overall Gleason score for the tissue sample based on which Gleason grade was assigned to the largest area and to the second largest area of the tissue.
Manually grading prostatic tissue is difficult because the pathologist must consistently evaluate a large number of cancerous areas on a highly magnified image of stained tissue. The pathologist may not miss any cancerous area. Moreover, the pathologist must consistently evaluate the gland arrangement and the shapes of individual glands in the various areas of a tissue slide as well as on other tissue slides in order to obtain an accurate Gleason score.
A method is sought for increasing the accuracy of Gleason grading performed on stained prostate tissue by reducing the inconsistencies and missed areas that commonly occur with manual grading.